First os version with ABI number and working system calls

assembly/applications/README.md

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+# Pat80 Applications
+
+## Intro
+This folder contains some example applications.
+The folder `brief` contains little applications that can be entered directly via keyboard in the memory monitor.
+The folder `big` contains complete applications to be loaded via sdcard or tape.
+
+## How to write an application
+When the Pat80 operating system is built, a `abi-generated.asm` file is built along with the rom binary. This file contains the description of the OS available API.
+An application targeting the last version of the OS should include this file, to make the system calls labels available inside the application code.
+The application can obtain the operating system ABI version (ABI -> https://en.wikipedia.org/wiki/Application_binary_interface) via the Sys_ABI call (it is a 16 bits integer returned in BC).
+The application's first command should be an ABI check: if the OS version is not compatible with the app, the app should exit displaying an error message.

assembly/applications/brief/hello_world.asm

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+org 0xA000
+include '../../bios/abi-generated.asm'
+
+STRING: DB "Hello",0
+ld bc, STRING
+call Sys_Print
+jp 0

assembly/applications/call_printc.asm

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-ld bc, 0xA000
-call 0x0010
-jp 0

assembly/applications/halt_test.asm

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-org 0x00A0
-
-test:
-nop
-nop
-nop
-nop
-nop
-jp test

assembly/applications/hello_world.asm

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-; Prints "Hello world" in terminal
-; Usage: assemble this file with z80asm and insert the resulting bytes
-; via Memory Monitor from address 0xA000 to test SET and RUN commands.
-
-org 0xA000  ; Set starting position to ram
-ld bc, HELLO_WORLD_STR
-Term_print:
-    ld a, (bc)  ; bc is the pointer to string's first char
-    cp 0        ; compare A content with 0 (subtract 0 from value and set zero flag Z if result is 0)
-    jp z, term_print_end
-    out (0x00),a    ; output char to IO device 0, addr 0
-    inc bc ; increment bc to move to next char
-    jp Term_print
-	term_print_end:
-	halt
-HELLO_WORLD_STR: DB "Hello world!",0